The present invention relates in general to subjecting a workpiece to a series of manufacturing operations, and, more specifically, to the machining of parts or workpieces by a plurality of machining stations using fixtures transported by a gantry system.
In the manufacturing of certain cast metal products, it is not possible to achieve the final part shape and tolerances by casting alone. Part manufacture usually includes several machining operations that must be applied to the original casting, such as drilling, boring, milling, cutting, and tapping. Products of this type include engine manifolds, wheels, brake rotors, and suspension components such as steering knuckles, control arms, and cross members.
In mass production, it is necessary to organize a manufacturing process with high reliability, short cycle times, easy maintenance, and worker safety while minimizing cost and space requirements. It is also highly desirable to achieve flexibility of the manufacturing process and the manufacturing equipment so that the process and equipment can be adapted at low cost to changes in part design, part mix, or part quantities.
Manufacturing systems utilizing automation are preferred because of increased consistency and reduced time and cost. Automated machining stations typically receive a workpiece (e.g., an unfinished casting) mounted on a fixture (also called a pallet) and automatically perform the desired machining operations on the workpiece. The workpieces may be delivered to and removed from the machining station either manually or automatically by a conveyance.
Various types of machining stations are known. Dedicated stations are constructed to perform a fixed set of operations and cannot be easily adapted to perform other tasks. Dedicated stations usually have a cost advantage when a large volume of parts is to be made and no significant design changes are to occur during a long production run. Another type of station is the computer-numerically-controlled (CNC) machine, which is programmable to perform a variety of machining operations and has advantages of being able to produce parts with a lower number of machining stations and therefore requiring less relocation of a workpiece during manufacture. In addition, CNC machines are more easily adapted to new products or processes and can reduce overall capital investment for a changeover. A typical CNC machine has programmable multidimensional movement of both the tool head and the table that receives the fixture and workpiece.
An especially adaptable type of CNC machine is the flex turret cell which employs a multi-spindle head that automatically reconfigures itself to use selected ones of several tools contained on the multi-spindle head. The multi-spindle head usually comprises a gearbox with multiple output shafts (a different tool on each shaft) driven by a common input shaft. The head is indexed between separate operations while a workpieces remains at the machining station, which improves cycle time and accuracy.
Nevertheless, previous automated systems have suffered from various drawbacks. For example, transfer of workpieces between work stations has remained labor intensive, slow, and/or inflexible (i.e., not easily adaptable to process changes or substitutions). A single workpiece may need to be swapped between various fixtures corresponding to different machining stations when the particular set of machining operations to be performed on the workpiece occurs at several different machining stations. Overall accuracy suffers due to a loss of an exact registration in a reference position between fixtures. Another disadvantage has been the inaccessibility of the CNC machines during operation, making observation and maintenance more difficult.
These disadvantages are overcome by the present invention.
It is an object and advantage of the present invention to provide a flexible manufacturing line and manufacturing process providing flexibility and adaptability to variation, improved maintenance of reference position on the fixture during manufacture, improved accessibility to machining stations during operation, and increased safety.
In one aspect, the present invention provides apparatus of applying a series of machining operations to a workpiece. The apparatus comprises an operator station for affixing workpieces to respective fixtures, the-fixtures registering and retaining the workpieces during the series of machining operations. There are a plurality of machining stations, each machining station being configured to receive the fixtures and performing respective machining operations. A gantry system includes a plurality of movable carriages running proximate to the machining stations and the operator station. The gantry system receives the fixtures for conveyance between and among the operator station and the machining stations. A main controller communicates with the operator station, the plurality of machining stations, and the gantry system. The main controller monitors status of the workpiece and is programmed with a sequence for applying predetermined ones of the machining operations to the workpiece. The main controller commands the gantry system to convey the fixture to at least one of the machining stations, commands the one machining station to perform a selected one of the machining operations, and commands the gantry system to return the fixture to the operator station.